Dynamic laminating method and apparatus for ultrasonically bonding juxtaposed webs

ABSTRACT

A method and apparatus for bonding together a plurality of juxtaposed webs which are subject to being ultrasonically bonded together to form a laminate as the webs are being driven forward at a relatively high velocity. The regions of the webs to be bonded are subjected to progressively increasing compressive forces while simultaneously being subjected to ultrasonic energy as they traverse an elongate portion of a predetermined path at a predetermined velocity. After the regions are ultrasonically bonded they may be subjected to another compression prior to the bonds becoming fully set upon cooling. The method may be practiced in an apparatus which includes an ultrasonic horn and an anvil which are configured and disposed to define a bonding passageway having an elongate convergent portion; and the apparatus may include a pressure roll biased towards the anvil adjacent the downstream end of the passageway. In a preferred apparatus embodiment: the anvil is a power-rotated cylinder having a relief-type bonding pattern disposed on its circumferential surface, and the face of the ultrasonic horn is so curved in the machine direction that the passageway has a convergent-divergent arcuate shape; the entrance to the passageway is sufficiently high to obviate web-splice induced jams; and the convergent portion of the passageway is preferably somewhat longer in the machine direction than the divergent portion.

TECHNICAL FIELD

This invention pertains to ultrasonically bonding togetherwebs--particularly thin flexible webs--to form a flexible laminatethereof which webs are, corporately, subject to being ultrasonicallybonded together: preferably pattern bonded together. Such webs include,for example, fibrous non-wovens of such materials as polyesters, andpolypropylene; thermoplastic films; and elastomeric films comprisingsuch materials as butadiene/styrene and copolymers. More particularly,this invention pertains to such ultrasonic laminating which is effectedon-the-fly: that is, while the webs are being forwarded in juxtaposedrelation at a relatively high velocity.

BACKGROUND ART

Prior ultrasonic bonding apparatuses include apparatuses for covertingweb or sheet materials into laminates on-the-fly with predeterminedpatterns of bonded regions. Such apparatuses are disclosed, for example,in U.S. Pat. No. 3,562,041--Robertson; and U.S. Pat. No. 3,733,238--Longet al.

Robertson discloses that the working tip preferably be straight [i.e.,flat] or tapered in the downstream direction for smooth entry andpassage of the objects but, concomitantly, that there be a minimum areaof contact between the working tip and the anvil or back-up. Withrespect to such apparatus having an anvil cylinder, the patent teachesthat the tip have either a tangent relation to the anvil, or be taperedin the direction of rotation to provide greater convergence wheredesired than a tangent relation. This patent also disclosesintermittently forming a wider gap between the working tip and the anvilto facilitate the entry and passage of materials between them.

U.S. Pat. No. 3,733,238--Long et al provides plural ultrasonic hornswhich are shown in the figures to have flat faces, and which horns areoffset in the machine direction.

While the background art discloses methods and apparatus which have beendeveloped to overcome some of the problems of ultrasonically bondingwebs to convert them into laminates--particularly pattern bondedlaminates--the discovered background art has not solved all of theproblems associated with such web laminating in the manner of nor to theextent of the present invention. In particular, but not intending tothereby limit the scope of the present invention, providing amachine-direction elongate ultrasonic bonding passageway in which thewebs are progressively subjected to increasing compressive forces over asubstantial distance in the machine direction as they traverse thebonding passageway and which bonding passageway preferably has asufficiently high upstream opening to obviate websplice-induced jams.

DISCLOSURE OF THE INVENTION

In accordance with one aspect of the invention, a method is provided fordynamically ultrasonically bonding a plurality of webs together whilethey are being forwarded in juxtaposed relation along a predeterminedpath at a predetermined velocity, and which webs are subject to beingultrasonically bonded into a laminate having bonded regions. The methodcomprises the step of subjecting the portions of the webs which are tobe bonded to progressively increasing compressive forces along anelongate portion of the path, which compressive forces are derived frombiasing an ultrasonic powered ultrasonic horn towards a driven anvil. Ina preferred embodiment the elongate portion of the web path has amachine-direction length of about fifty or more times the sum of theuncompressed thicknesses of the webs; and more preferably aboutone-hundred times or more. The method may also include the step ofsubjecting the bonded regions of the laminate to post-bondingcompression before the bonds become fully set upon cooling. Apparatusembodiments of the invention may provide a bonding passageway which isarcuate-shape and converges in the downstream direction over aconcomitantly elongate, circumferentially extending portion of acylindrical, powered anvil, the convergence being from an entranceheight which is greater than the total uncompressed thicknesses of thewebs to a virtually contacting relation; and may further include adivergent portion downstream from the convergent portion. Preferably,the entrance height is from about one to about four times the sum of theweb thicknesses, and more preferably, from about one to about two timessuch sum. The horn face may be of a uniform radius greater than theradius of the anvil cylinder and disposed to provide the passageway witha longer convergent portion than divergent portion. The apparatus mayfurther include a relatively non-deformable, rotatably mounted pressureroll which is biased towards the anvil adjacent the downstream end ofthe bonding passageway.

BRIEF DESCRIPTIONS OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter regarded as forming thepresent invention, it is believed the invention will be betterunderstood from the following description taken in conjunction with theaccompanying drawings in which:

FIG. 1 is a partially schematic, fragmentary side elevational view of anexemplary apparatus embodiment of the present invention.

FIG. 2 is an enlarged scale, fragmentary plan view of elements of arepresentative, relief type bonding pattern disposed on the cylindricalsurface of the anvil cylinder of the apparatus shown in FIG. 1.

FIG. 3 is an even more greatly enlarged scale, fragmentary view of aportion of the relief-type bonding pattern shown in FIG. 2.

FIG. 4 is an enlarged side elevational view of the ultrasonic horn andanvil cylinder of the apparatus shown in FIG. 1, but in which FIG. 4 theelements are non-uniformly scaled for the purpose of visibly showingtandemly disposed convergent and divergent portions of the bondingpassageway disposed between the horn-face and the anvil cylinder.

FIG. 5 is a sectional view of the ultrasonic horn shown in FIG. 4 andtaken along line 5--5 thereof for the purpose of showing that thehorn-face has a rectilinear planform.

FIG. 6 is a graph showing the clearance relation between an exemplaryhorn-face and an exemplary anvil cylinder such as shown in FIG. 4; and,by way of comparison, the corresponding clearance between a flat-facedhorn and the same anvil cylinder.

DETAILED DESCRIPTION OF THE INVENTION

An exemplary web laminating apparatus 20 embodying the present inventionis shown in FIG. 1 to include a frame 21 (only part of which is shown);an ultrasonic power device 22 comprising an ultrasonic transducer 23,amplifier 24, and ultrasonic horn 25; a pivotally mounted frame assembly26 pivoted on bearing 27 and upon which the ultrasonic power device 22is adjustably mounted; a rotatably mounted anvil cylinder 29 havingrelief-type patterned areas 34, and non-bond inducing areas 36; anvildrive means 30; actuator means 31 for biasing the ultrasonic horn 25towards the anvil cylinder 29; contact-point adjustment means 33,camming means 37 for spacing the ultrasonic horn 25 outwardly from theanvil cylinder 29 while the non-bond-patterned areas 36 of the anvilcylinder 29 pass the ultrasonic horn 25; post-bonding compression means38; tension isolating means 40; guide rolls 41, 42 and 43 for guidingthree webs 44, 45 and 46, respectively, onto the anvil cylinder 29; andguide roll 47 for guiding the laminated web 50 to downstream ancillaryapparatus such as, for instance, reeling means not shown. The apparatusmay further include means for forwarding the webs under controlledtension, which means are well known to persons of ordinary skill in theart, and which means are not shown for the purpose of enhancing theclarity of FIG. 1.

Briefly, when the exemplary apparatus 20, FIG. 1, is operated, webs 44,45 and 46 which are subject to being ultrasonically bonded together areforwarded onto the power-rotated anvil cylinder 29 having acircumferential velocity which is preferably from about seventy to aboutfour-hundred meters per minute; pass through a pressure biased,ultrasonic bonding passageway between the ultrasonic horn 25 and theanvil cylinder 29 where they are subjected to ultrasonic vibrationalenergy whereupon predetermined patterned regions of the webs becomebonded regions in laminate 50; the bonded regions of laminate 50 aresubjected to post-bonding compression by means 38 to enhance the bonds;and the portion of laminate 50 disposed on anvil cylinder 29 is isolatedfrom downstream tension by means 40.

As is more fully described hereinafter, the horn-face 51 of ultrasonichorn 25 has a curvilinear-shape which is so configured and disposed withrespect to bond-pattern defining elements disposed on the surface ofanvil cylinder 29 that an arcuate-shape bonding passageway is definedtherebetween to have a convergent entrance portion in tandem relationwith a divergent exit portion. The curvature of the horn-face 51 is sorelated to the radius of the anvil cylinder 29 that the passageway has asubstantial machine-direction-elongate active length over which activelength the webs will be acted on compressively by the inwardly biasedultrasonic horn; and the ultrasonic horn is so disposed that theconvergent portion preferably has a somewhat greater machine-directionlength than the divergent portion of the passageway. By making theheight of the entrance to the passageway from one to four times the sumof the uncompressed thicknesses of the webs, and the active length ofthe passageway preferably about fifty or more times and, morepreferably, one-hundred or more times the sum of the uncompressedthicknesses of the webs, bonding will occur over substantial lengths ofmachine-direction web travel. Also, while not intending to be bound by atheory of operation, it is believed that such a bonding passagewayhaving such a machine-direction-elongate active length enables theultrasonic horn to function as a vice at ultrasonic frequency tocyclically stop the upper surface of the outermost web 44 while thedriven anvil continues to advance the inner surface of the innermost web46. This induces shear strains in the webs at the ultrasonic frequencyof the ultrasonic horn 25. Thus, the total bonding energy is derivedfrom the sum of the ultrasonic compressive-strain hysteritic lossesinduced by the ultrasonic horn per se, and the ultrasonic shear-strainhysteritic losses induced by the horn clamping and anvil rotation. It isfurther believed that by thus supplying hysteritic loss energy from theanvil cylinder drive means enables the use of a lower power ultrasonictransducer than would otherwise be required; and, at least for someapplications, makes the bonding quality of the apparatus relativelyinsensitive to anvil velocity over a substantial velocity range.

FIG. 2 is a fragmentary plan view of a relief-type patterned area 34 ofanvil cylinder 29, FIG. 1. Pattern elements 53 are elongate in themachine-direction and have wide regions 54 spaced apart in the machinedirection by narrow connecting runners. Pattern elements 55 are spacedin the machine direction and have discshape faces. Pattern elements 53and 55 extend radially outwardly from the remainder of the surface 56 ofthe patterned portion 34 of anvil cylinder 29; and may be madeintegrally with anvil cylinder 29 or discretely made and then secured tosurface 56.

FIG. 3 is a fragmentary enlarged scale view showing the smoothly curvedshape of a wide region 54 of an elongate pattern element 53.

FIG. 4 (not a scale view) shows the side-elevational spatialrelationship of the ultrasonic horn 25 and the anvil cylinder 29 of theexemplary apparatus 20, FIG. 1, in a spaced apart relation as thoughwebs (not shown) were in fact present. In FIG. 4, the ultrasonic horn 25has a machine-direction length designated MDL, and the horn-face 51 hasa radius designated RH which is drawn coincident with the imaginaryaxial centerline of the ultrasonic horn 25; the anvil cylinder 29 has aradius designated RA which, as drawn, is parallel to RH; and theultrasonic horn 25 is so asymmetrically disposed with respect to anvilcylinder 29 that their closest points (i.e., the points which would bein contacting relation were webs not present) are aligned with thecommon radius designated RC. Thus, the common radius RC is angularlyoffset from the radius RA by the angle designed B; and the axialcenterline of the ultrasonic horn 25 is spaced forwardly (i.e., in theupstream direction) of the axis of rotation of the anvil cylinder 29 bya distance designated OS. Thus, an arcuate-shape bonding passagewaydesignated 58 is defined intermediate the horn-face 51 and the adjacentsurface portion of the anvil cylinder. As drawn, not to scale,passageway has a visibly convergent entrance portion designated 59, anda visibly divergent exit portion designated 60 albeit, were preferredembodiments drawn to scale, such convergence and divergence would notgenerally be visibly noticeable. However, such convergence anddivergence are desirable--indeed the convergence is essential--and theasymmetrical offset enables the cantilevered tip of the ultrasonic horn25 to be somewhat displaced circumferentially of the anvil cylinder bydrag forces without precipitating serious deliterious consequences. Thatis, when drag forces so displace the horn tip, the point of closestapproach of the horn-face to the anvil surface effectively rollsupstream (i.e., changing offset OS and angle B, FIG. 4) without having asubstantial effect on either the geometry of the active length portionof the passageway 58 or its entrance height EH. For example, in apreferred embodiment, a change in OS of about one millimeter changes theentrance height EH by less than about one-fortieth of a millimeter.

FIG. 5 is a reduced scale sectional view taken along line 5--5 of FIG. 4for the purpose of showing the solid construction of ultrasonic horn 25,and the rectilinear shape of the planform of its horn-face. Thecross-machine-direction width of the ultrasonic horn 25 is designatedMDW.

FIG. 6 is a graph on which line 65 represents the clearance between anexemplary ultrasonic horn 25 and anvil cylinder 29 for practicing thepresent invention to ultrasonically bond an elasticized trilaminate 50consisting of a nonwoven polyester top web 44 having a nominal thicknessof about eighteen-hundredths of a millimeter an elastomericbutadient/styrene copolymer second or middle web 45 having a nominalthickness of about four-hundredths of a millimeter and elongated aboutone-hundred percent; and a polyethylene third or bottom web 46 having anominal thickness of about three-hundredths of a millimeter. For thistrilaminate application of the present invention, the ultrasonic horn 25had a MDL, FIG. 5, of about seven centimeters, a MDW, FIG. 5, of aboutfive centimeters; a horn-face 51 having a radius RH, FIG. 4, of aboutseventeen centimeters; was made of titanium; and was powered with aBranson Model 186P fourteen-hundred-watt power supply driving anultrasonic transducer 23 (Branson converter Model 802), and fitted witha two-and-one-half to one amplifier 24 (Branson booster for a Model 401actuator). Concomitantly, anvil cylinder 29 had a radius RA, FIG. 4, ofabout fifteen-and-one-quarter centimeters and a relief pattern of thegeneral configuration shown in FIGS. 2 and 3. The pattern elements 53and 55 had radially extending heights of about one-half millimeter. Theultrasonic horn 25 was disposed with respect to the anvil cylinder asgenerally shown in FIG. 4 with an offset OS of about three millimetersand an offset angle B of about three degrees which offsets were setthrough the use of the contact-point adjustment means 33, FIG. 1. Theclearance between the horn-face 51 and the anvil cylinder 29 was thencalculated along the circumferential length of the passageway 58, FIG.4, and plotted to generate line 65. The points designated 71 through 76are, respectively: point 71 is the entrance to passageway 58, FIG. 4,having a net (without webs being present) entrance height EH orclearance of about seven-tenths of a millimeter; point 72 which is thepoint of initial contact of the three juxtaposed webs with thehorn-face; point 73 at which point the webs have become sufficientlymanually compressed to effectively commence being heated by thevibratory energy supplied by the ultrasonic horn; point 74 which is thepoint of closest approach of the horn-face to the anvil cylinder (i.e.,to the pattern elements on the anvil cylinder) and is indicated to havea clearance of about twenty-five microns (one-thousandth of an inch);point 75 which is the point at which the trilaminate 50, FIG. 4, losescontact with the horn-face 51 and which is indicated to have a clearanceof about fifty microns (two-thousandths of an inch); and point 76 is theexit of passageway 58, FIG. 4, having an indicated net height EE (i.e.,without webs) of about three-tenths of a millimeter. Thus, as the aboveindentified webs 44, 45 and 46 pass between the horn-face 51 and theanvil cylinder 29, FIG. 1, they are in contact with the horn-face frompoint 72 to point 75 which is a machine-direction distance (contactlength CL) of about three centimeters; they are mechanically compressedas they travel from point 72 to point 73; progressively compressed andultrasonically heated as they travel from point 73 to 74; experiencediminishing ultrasonic heating and diminishing compression as theytravel from point 74 to point 75 whereat contact with the horn-face islost. Thus, in this configuration, the contact length CL of thepassageway is about three centimeters, and the ultrasonically activelength AL is about two-and-one-half centimeters. Such an apparatus hasbeen found to be very effective for bonding such a trilaminate at speedsin the range of from about ninety meters per minute to abouttwo-hundred-fifty meters per minute although it is not intended tothereby imply a limitation of the present invention. Also, however, inthis speed range the bonding of the exemplary trilaminate was found tonot be very sensitive to speed changes. That is, over this speed range,bonds of relatively uniform strength were obtained by only adjusting thehorn bias a relatively small amount. By way of comparison with line 65,line 80 is the clearance between a prior-art flat faced ultrasonic hornand the same anvil cylinder discussed. As shown in FIG. 6, such aflat-face/anvil configuration has a much steeper convergence anddivergence, and a much shorter machine-direction active length. Suchsteeper convergence is more apt to precipitate web tearing at highmachine speeds; and the shorter active length further limits theeffective speed at which the apparatus can operate.

Referring again to FIG. 1, camming means 37 are provided to mechanicallyspace the horn-face 51 from the anvil cylinder while unpatterned areassuch as areas 36 of the anvil cylinder 29 pass under the horn-face toobviate damage to the apparatus. Thus, the need for such camming meanswould be obviated if the anvil cylinder has a continuous bonding patterndisposed on its cylindrical periphery; and the need for such cammingmeans would be substantially vitiated if alternate means (not shown)were provided for interrupting the ultrasonic power and/or the horn biasas unpatterned portions of the anvil cylinder pass the ultrasonic horn.In this event, the entrance height EH of the bonding passageway shouldbe sufficient to cause the horn-face to ride up and over and threshholdend portions of the pattern elements to obviate damaging the ultrasonichorn and the pattern elements.

Still referring to FIG. 1, the laminate 50 emerging from betweenhorn-face 51 and anvil cylinder 29 is subjected to post-bondingcompression by means 38.

Post-bonding compression means 38, FIG. 1, comprises a pressure roll 90,a lever arm 91, an actuator 92, and an adjustable innermost-travel-stopmeans 93 comprising an adjustment bolt 94. The lever arm 91 is rotatablymounted on pivot pin 95, the rod 96 of actuator 92 is pinned to thelever arm by pivot pin 97; the base of the actuator 92 is pivotallyconnected to the frame of the apparatus by pivot pin 98, and thepressure roll 90 is rotatably secured to the lever arm 91 on shaft 99.In operation, the actuator 92 is powered to bias the pressure roll 90towards the anvil cylinder with a predetermined but adjustable force;and the adjustment bolt 94 is adjusted to provide a touching but notpressure loaded contact between the pressure roll 90 and the anvilcylinder in the absence of a laminate 50. Thus, a laminate will besubjected to the full predetermined force, and the predetermined forcewill be distributed on the bonded regions of the laminate.

In the exemplary embodiment of apparatus 20 described hereinabove, asteel pressure roll having a diameter of about seven-and-one-halfcentimeters was provided and was biased with a force of up to aboutforty kilograms per lineal centimeter of machine width (i.e., the lengthof the pressure roll). By virtue of being steel, this pressure roll wassubstantially non-deformable when biased. Thus, the biasing force--thepost-bonding compression force--was limited to the bonded regions of thelaminate disposed between the pattern elements on the anvil cylinder andthe pressure roll. This effectively increased the peel strength of thetrilaminate described above. Again, while not intending to be bound by atheory of operation, it is believed that such a post-bonding compressionis especially effective for laminates comprising a non-woven web becauseit causes the fibers thereof to be virtually imbedded in the nextadjacent web (i.e., the elastomeric web in the exemplary trilaminatedescribed hereinabove).

The post-bonding compression described above enables the apparatusoperator some latitude in setting the biasing force for the ultrasonichorn (i.e., actuator 31) and the biasing force for the pressure roll(i.e., actuator 92) to precipitate bonds having satisfactory peelstrengths. That is, generally speaking, horn biasing may be lowered ifpressure roll bias is increased. Inasmuch as high horn bias canprecipitate perforations, and high rates of horn wear, or otherundesirable effects, the pressure roll bias enables the apparatusoperator to maintain a non-deleterious low level of horn bias and stillachieve satisfactory bonds by applying sufficient post-bondingcompression.

Tension isolating means 40, FIG. 1, are provided for the purpose ofisolating the portion of laminate 50 disposed upstream therefrom fromthe level of tension applied to the laminate 50 downstream from means40. In some applications, such means are optional: that is, such meansare optional where the level of downstream tension is insufficient tootherwise precipitate deliterious consequences with respect to issuing asatisfactorially bonded laminate 50 from the apparatus.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. Moreover, whilethe invention has been illucidated by describing an exemplarytrilaminate, it is not intended to thereby preclude bilaminates andlaminates of greater than three plies from the scope of the invention.Therefore, it is intended to cover in the appended claims all suchchanges and modifications that are within the scope of this invention.

What is claimed is:
 1. A method of dynamically ultrasonically bondingtogether a plurality of webs while they are being forwarded injuxtaposed relation along a predetermined path at a predeterminedvelocity, and which webs are subject to being ultrasonically bonded intoa laminate having bonded regions, said method comprising the steps of:subjecting the portions of said webs to be bonded to progressivelyincreasing compressive forces along an elongate portion of saidpredetermined path, said compressive forces being derived from biasingan ultrasonically powered ultrasonic horn towards a driven anvil;applying sufficient ultrasonic power and biasing to said ultrasonic hornto effect said bonding; forwarding said laminate from under the actionof said horn-biasing induced compressive force; and then subjecting onlysaid bonded regions of said laminate to a substantial post-bondingcompression prior to the bonded regions becoming fully set.
 2. A methodof dynamically ultrasonically bonding together a plurality of webs whilethey are being forwarded in juxtaposed relation along a predeterminedpath at a predetermined velocity, and which webs are subject to beingultrasonically bonded into a laminate having bonded regions, said webcomprising one web and a second web, said second web comprising anelastomeric film, said method comprising the steps of: subjecting theportions of said webs to be bonded to progressively increasingcompressive forces along an elongate portion of said predetermined path,said compressive forces being derived from biasing an ultrasonicallypowered ultrasonic horn towards a driven anvil; applying sufficientultrasonic power and biasing to said ultrasonic horn to effect saidbonding; and elongating said second web in the machine direction up toabout one-hundred-fifty percent prior to said bonding and constrainingsaid second web to remain so elongated during said bonding.
 3. Themethod of claim 2 further comprising the steps of forwarding saidlaminate from under the action of said horn-biasing induced compressiveforce, and then subjected the bonded regions of said laminate to asubstantial post-bonding compression prior to the bonded regionsbecoming fully set.
 4. A method of dynamically ultrasonically bondingtogether a plurality of webs while they are being forwarded injuxtaposed relation along a predetermined path at a predeterminedvelocity, and which webs are subject to being ultrasonically bonded intoa laminate having bonded regions, said webs comprising one webcomprising an interfilamentary bonded fibrous material, a second webcomprising an elastomeric film, and a third web comprising apolyethylene film, said second web being disposed intermediate said oneweb and said third web, the total uncompressed thicknesses of said websbeing about one-quarter millimeter or less, and said predeterminedvelocity being from about seventy meters per minute to aboutfour-hundred meters per minute, said method comprising the steps of:subjecting the portions of said webs to be bonded progressivelyincreasing compressive forces along an elongate portion of saidpredetermined path, said compressive forces being derived from biasingan ultrasonically powered ultrasonic horn towards a driven anvil; andapplying sufficient ultrasonic power and biasing to said ultrasonic hornto effect said bonding.
 5. The method of claim 4 further comprising thesteps of forwarding said laminate from under the action of saidhorn-biasing induced compressive force, and then subjecting the bondedregions of said laminate to a substantial post-bonding compression priorto the bonded regions becoming fully set.
 6. The method of claim 4 or 5wherein said one web comprising fibrous material is disposedintermediate said ultrasonic horn and said second web during saidbonding.